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lALEXAHDER  nADlE 


LIBRARY 

UNIVERSITY  OF 

CALIFORNIA 

SANTA  CRUZ 


i. 


THE 

CLOUDS  AND  FOGS 
OF  SAN  FRANCISCO 


N 


I 


I 


"C^«  (Brain  Pauttbd  by  Arthur  F.  Mathbws 

**From  Ocean* J  breast  to  the  expectant fieldj  I  come"* 


THE 

CLOUDS  AND  FOGS 
OF  SAN  FRANCISCO 

BY 

ALEXANDER  McADIE 


SAN  FRANCISCO 

A.  M.  ROBERTSON 

MCMXII 


COPYRIGHT  BY 

M.  ROBERTSON 
1912 


SAN  FRANCISCO 


M5 


M.  R.  B.  M. 


CONTENTS 


The  Clouds 1 

Cloud  Effeds          ....  8 

Cloud  Names 16 

Cloud  Measurements       ...  32 

Tracking  the  Clouds   ....  38 

The  Fogs 48 

Types  of  Fog     .....  53 

Sunshine  and  Fog   ....  61 
Percentage  of  Sunshine  at  Mt.  Tamalpais 

13  Years  Records  to  1910-11        .  67 
Percentage  of  Sunshine  at  San  Francisco 

18  Years  Records  to  1910-11    .  68 

The  Fog  Curtain  and  the  Sun  .         .  71 

Fog  and  Equivalent  Rain      ...  73 

Past  and  Future  of  the  Fog       .         .  78 

Sixty-two  Years  of  Rainfall                     .  89 
Tables  Showing  Monthly,  Seasonal  and 

Annual  Rainfall     .  95-106 


ILLUSTRATIONS 

PAGB 

The  Grain     ....  Frontispiece 

Nurslings  of  the  Sky.     Cirro-cumuli  .  5 

The  saver  Lining        .         .         .         .10 

Interfret  Clouds       ....  21 

Cirrus-nebula       .  .  .  .  .27 

Cirro-stratus   .  .  .  .  .  33 

Cirro-cumuli  ....        39 

Cirro-cumuli  one  minute  change         .  39 

Cumuli       ......       45 

Changing  Alto-cumuli        .  .  .  51 

Changing  Alto-cumuli  one  minute  later      .        5 1 

»  How  the  Fog  Comes  In  at  San  Francisco      57 

•  Fog  Cascades      .....       63 

•  Fog  Surges 69 

•  Morning  Fog  over  the  Valleys       .         .       75 
'  Fog  Pyramid  from  Mt  Tamalpais    .  81 

•  Above  the  Fog  ,         ...       87 

•  Helmholtzian  Fog  Billow         .         .  93 
Chart  of  Seasonal  Rainfall  at  San  Fran- 
cisco for  Sixty-two  Years           .         .       99 

Fog  Changing  to  Cloud,  San  Francisco 
Bay 103 


THE  CLOUDS. 

URSLINGSoftheSky" 
the  clouds  have  been 
called.  The  phrase  is 
Shelley's  but  the  thought 
is  as  old  as  mankind. 
For  when  the  first  man  woke  to 
consciousness  of  beauty  in  the  life 
around  him,  looking  upward  he 
found  there  also  forms  of  grace. 
*' Children  of  the  Sky''  they  must 
have  seemed  to  him.  Perhaps  in 
the  beginning  he  doubted  their 
harmlessness  and  watched  with 
some  trepidation  the  cloud  shadows, 
at  times  lingering  as  if  to  caress  the 
hills  and  again  passing  on  more 
rapidly  than  swiftest  birds.  Then 
reassured    and    bilder    grown,    he 


2         THE  CLOUDS  AND  FOGS 

walked  about  unmindful  of  the  sky 
creatures,  nor  did  he  heed  them 
save  when  at  sunrise  and  again  at 
close  of  day,  his  barbaric  indiffer- 
ence yielded  to  the  power  of  beauty. 
Compelled  then  to  notice  and  re- 
sped:,  his  fancy  peopled  the  sky 
with  beings  mysterious  as  the  clouds 
themselves.  In  that  order  of  exis- 
tence so  different  from  his  own,  his 
untutored  mind,  ere  long 

Saw  God  in  clouds  and  heard  Him 
in  the  wind. " 

It  is  a  far  cry  from  primitive  man 
to  the  out-of-doors  man  of  today: 
yet  if  the  truth  be  told  there  is  no 
great  disparity  in  their  knowledge 
of  clouds.  It  may  hurt  our  pride  to 
confess  it,  but  most  of  us,  mountain- 
eers and  mariners  included,  are  only 
nephelolaters,  cloud  admirers  and 
nothing  more.  Few  read  in  a  cloud 
a  story  of  birth,  growth  and  dissolu- 


OF  SJN  FRANCISCO  3 

tion,  a  sequence  not  without  signifi- 
cance to  men.  In  the  Ufe  history 
of  each  nomad  of  the  sky  there  is  a 
wonder  tale  of  forces  operating  at 
various  levels  with  varying  intensi- 
ties. Each  deHcately  poised  mass 
illustrates  physical  processes,  which 
harnessed  in  the  steam  engine  have 
determined  the  destiny  of  nations. 
So  much  do  we  seem  to  know  of 
the  expansive  power  of  water  vapor 
when  thus  at  work  for  the  weKare 
of  man,  yet  so  Uttle  do  we  know  of 
this  same  expansion  and  condensa- 
tion when  in  the  free  air. 

We  of  the  West  glory,  not  with- 
out reason,  in  the  achievements  of 
our  engineers.  For  irrigation  work 
and  in  the  utilization  of  water  power, 
great  dams  and  mighty  reservoirs 
have  been  built.  We  impound  and 
imprison  the  impetuous  floods  upon 
the  mountain  side  until  such  time  as 
comes  the  call  to  spread  the  water 


4  THE  CLOUDS  AND  FOGS 

o'er  a  thirsty  land.  Think  what  the 
clouds  do !  Reservoirs  of  vast  capa- 
city, though  plastic  and  seemingly 
of  flimsiest  construction,  they  form 
and  dissolve  before  one's  eyes.  But 
ever  the  load  of  life-giving  water  is 
lifted  from  the  level  of  the  sea  to 
the  peaks  of  the  highest  mountains 
and  if  need  be,  beyond.  The  cas- 
cades that  charm  us,  the  rushing 
streams  of  the  mountains,  the  mantle 
of  white  covering  the  '*Ultimae 
Sierra",  all  are  children  of  the 
clouds  and  owe  their  being  and 
their  place  to  these  wandering  res- 
ervoirs. 

Though  the  clouds  pass  hourly 
before  us,  we  know  comparatively 
little  about  cloud  structure.  An 
elementary  knowledge  of  cloud  for- 
mation will  not  be  without  value,  and 
the  ability  to  even  partially  decipher 
the  meaning  of  a  given  cloud  mass 
will  not  only  diredtly  benefit  us,  but 


1 


OF  SAN  FRANCISCO  7 

will  add  much  to  our  appreciation 
of  the  clouds'  beauty.  Back  of  each 
form  of  grace,  the  intelligent  obser- 
ver will  be  able  to  trace  controlling 
laws,  developing  and  unfolding  the 
mass  of  globules,  breathing  life  as 
it  were  into  the  inanimate  vapor. 
Therefore  let  us  study  these  nurs- 
lings of  the  sky,  even  where  they 
lie,  even  as  they  move  in  unending 
procession. 


CLOUD  EFFECTS. 


F  we  to-day  know  little 
about  the  clouds,  our 
predecessors  knew  still 
less.  The  cloud  was  an 
alien  and  cloud  effedis 
were  generally  misinterpreted.  Yet 
the  clouds  have  played  a  part  in 
history.  Many  a  mysterious  vision, 
many  a  special  revelation,  from  Bel- 
shazar's  feast  to  Luther's  encounter 
with  a  cumulo-nimbus  or  thunder 
cloud,  has  been  nothing  but  an  ex- 
traordinary cloud  effedl.  Many  a 
spiritual  awakening  too  has  come 
from  cloud  phenomena,  from  deep 
impressions  made  by  some  unusual 
slant  of  light  or  some  awe-inspiring 
cloud    shadow.     It    is    not    strange 


OF  SAN  FRANCISCO  9 

that  men,  especially  in  earlier  days, 
should  have  failed  to  perceive  and 
clearly  understand  such  effects.  For 
even  until  quite  recent  times,  those 
who  were  best  informed  concerning 
natural  phenomena  knew  little  about 
the  clouds  and  so  could  not  disprove 
popular  belief  that  all  strange  appear- 
ances were  directly  connected  with 
some  problem  of  the  time.  Look- 
ing for  a  sign,  it  was  most  natural 
that  imaginative  minds  should  trace 
in  unusual  cloud  phenomena,  the 
message  of  guidance  so  anxiously 
desired. 

Is  it  however  not  strange  that 
while  men  marvel  at  the  unusual, 
and  stand  awe-struck  before  any 
marked  manifestation  of  energy,  as 
when  the  lightning  leaps  from  cloud 
to  cloud,  they  seldom  lift  their  eyes 
from  the  commonplace  things  of 
life  to  the  never-ending  procession 
of  the  clouds?     There  they  might 


10       THE  CLOUDS  AND  FOGS 

read  messages  of  inspiration  and  de- 
light traced  with  exquisite  grace  in 
characters  of  purest  white  or  tinted 
with  the  gold  and  red  that  only 
cloudland  knows. 

Is  it  not  also  strange  that  the 
artist's  eye  does  not  always  follow 
nor  his  brush  perpetuate  the  grace 
of  form,  and  beauty  of  color  of  the 
clouds?  Speaking  generally,  few 
painters  concern  themselves  regard- 
ing the  accuracy  of  their  cloud 
effecfts.  *' Nothing  is  more  extraor- 
dinary in  Art ' ' ,  says  Professor  Clay- 
den,  in  his  well  known  book  on 
Cloud  Studies,  "than  the  general 
negled:  of  cloud  forms.  Many  of 
them  are  quite  as  worthy  of  careful 
drawing  as  the  leaves  of  a  tree,  the 
flowers  of  a  field,  the  ripples  on  a 
stream  or  the  texture  of  a  carpet  or 
marble  pavement.  Yet  it  is  the 
common  rule  to  find  pid:ures  which 
are  otherwise   marvellous  examples 


op  SAN  FRANCISCO  13 

of  skill  and  care,  disfigured  by  im- 
possible skies,  with  vague,  shapeless 
clouds  which  are  as  untrue  to  Nature 
as  it  would  be  possible  to  make 
them." 

We  need  not  exped:  the  artist  to 
be  a  cloud  expert  but  he  should  at 
least  know  enough  to  avoid  the 
introdudtion  of  clouds  due  to  as- 
cending currents,  forming  while  the 
day  grows  warmer,  in  sunset  or 
evening  scenes;  and  conversely,  the 
clouds  common  to  the  cold  hours 
or  formed  when  the  earth  is  losing 
heat,  should  not  appear  in  a  paint- 
ing representing  a  high  sun.  Some 
attention  should  be  paid  to  the  char- 
acter of  the  cloud  and  its  appropriate 
level.  Few  painters  get  their  clouds 
in  the  proper  level.  This  is  largely 
because  clouds  are  ever  changing 
and  vary  in  appearance.  Sometimes 
low  lying  clouds  will  resemble  clouds 
of  high  level;    but  a  keen  observer 


14       THE  CLOUDS  AND  FOGS 

can  deted:  differences,  though  often 
slight. 

When  all  is  said  and  done,  no 
painter  may  hope  to  do  full  justice 
to  the  clouds  of  sunrise  and  sunset 
nor  the  dazzling  radiance  of  mid- 
day. And  the  canvas  is  powerless 
to  hold  and  the  brush  tell  of  the 
inner  life  of  the  cloud,  its  begin- 
ning, its  culmination  and  its  dis- 
appearance. Only  to  him  who 
watches,  whether  it  be  from  attic 
window  or  from  mountain  height, 
is  it  given  to  know  the  clouds,  as 
they  pass  in  quiet  modesty  or  trail- 
ing glory. 

Perhaps  if  mankind  were  charged 
so  much  a  head  for  sunsets,  as  Stev- 
enson once  humorously  suggested, 
we  would  value  them  more  highly. 
Perhaps  too  if  we  had  to  pay  round- 
ly for  views  of  exquisite  cloudscapes 
or  travel  far,  as  we  do  to  see  land- 
scapes of  rare  beauty,  then  we  should 


OF  SJN  FRANCISCO  15 

so  construd:  our  habitations  and  so 
order  the  course  of  daily  cares,  as  to 
lose  nothing  of  the  scenery  of  the 
sky. 

And  the  gain  to  all  men  would  be 
beyond  measure. 


CLOUD  NAMES. 

HE  clouds  were  without 
names  until  the  begin- 
ning of  the  nineteenth 
century,  when  at  a  meet- 
ing of  the  Askesian  So- 
ciety, session  of  1802-3,  a  young 
chemist  of  Tottenham  read  an  essay 
in  which  he  proposed  a  cloud  classi- 
fication, using  the  terms  beginning 
with  the  lowest :  nimbus^  or  rain  ; 
stratus y  or  layer ;  cumulus,  or  rounded 
pile;  and  cirrus,  or  feather.  By 
combining  the  types,  all  ordinary 
cloud  forms  could  be  included. 
There  had  been  but  one  other  at- 
tempt at  cloud  classification.  How- 
ard's system  was  so  superior  to  this 
and  his  scheme  so  flexible  and  easy 

16 


OF  SJN  FRANCISCO  17 

of  comprehension,  that  it  met  with 
general  favor  and  ready  acceptance. 

Luke  Howard's  essay  was  reprint- 
ed in  1832,  translated  into  various 
languages  and  adopted  almost  with- 
out change  by  the  meteorological 
services  of  the  world.  While  his 
name  is  known  everywhere,  little 
has  been  handed  down  concerning 
the  man  himself.  I  find  that  he  is 
quaintly  described  on  the  title  page 
of  his  three  volumed  Climate  of 
London,  as  a  '*  Citizen  of  London, 
Honorary  Citizen  of  Madgeburg 
and  Honorary  Associate  of  the  Art 
Societies  of  Hamburg  and  Leipsic." 
No  less  a  person  than  Goethe  was 
among  those  who  were  charmed  by 
Luke  Howard's  work.  A  friend- 
ship sprang  up,  a  long  correspond- 
ence was  carried  on  and  the  poet 
sings  of  Howard  as  one  worthy  of 
all  honor. 

But  the  Howardian  nomenclature 


18 


THE  CLOUDS  AND  FOGS 


is  unscientific  in  that  it  classifies  ac- 
cording to  appearances,  and  with 
the  clouds  these  are  misleading. 
What  is  needed  is  a  system  showing 
the  origin  of  the  cloud.  Modern 
meteorology  cares  little  for  cloud 
beauty,  compared  with  significance 
in  the  matter  of  air  motion,  nucle- 
ation  and  thermal  energy  involved. 
Meteorology  wants  to  use  the  cloud 
as  an  exponent  of  the  rate  of  con- 
densation, a  means  of  measuring 
absorption  and  transportation  of  en- 
ergy. Howard's  system  gives  noth- 
ing of  these  and  indeed  it  is  doubtful 
if  it  ever  occurred  to  Howard  that 
clouds  would  one  day  be  studied 
with  spectroscope,  bolometer  and 
eleftrometer.  Within  the  past  five 
years  marked  advances  have  been 
made  in  studying  the  clouds  of  the 
sun.  At  Mount  Wilson,  Dr.  Hale 
and  his  colleagues  have  by  means  of 
the  spectro-heliograph  thrown  much 


OF  SAN  FRANCISCO  19 

light  upon  the  charadler  of  the  hy- 
drogen, calcium  and  other  clouds. 
Indeed  we  almost  know  more  of  the 
metallic  vapor  clouds  of  the  sun  than 
we  do  of  the  water  vapor  clouds  of 
earth. 

Preceding  Howard,  the  great 
naturalist  Lamarck  proposed  a  sys- 
tem for  cloud  classification,  but  like 
Howard's  it  was  based  largely  upon 
appearance.  Of  the  many  investi- 
gators following  Howard,  and  the 
list  is  a  long  one  embracing  various 
nationalities*  few  have  proposed  en- 
tirely new  systems.  Nearly  all  have 
simply  modified  the  Howardian 
types.  Many  elaborate  names  have 
been  proposed  but  in  the  main  these 
are  simply  descriptive  terms  Latin- 
ized.    Thus    no    less    than    sixteen 

*Poey,  Forster,  Clos,  Kaemtz,  Fritsch,  Jevons, 
Clouston,  Muhry,  Ley,  Weilbach,  Vettin,  Klein, 
Koppen,  Tissandier,  Barker,  M  oiler,  Toynbee,  Jesse, 
Abercromby,  Hildebrandsson,  Maze,  Singer,  Neu- 
mayer,  Kassner,  Clayden,  Clayton,  Gaster,  Vincent. 


20       THE  CLOUDS  AND  FOGS 

different  types  of  cirrus  have  been 
suggested  by  various  writers  and 
an  almost  equally  large  number  of 
sub  titles  for  both  the  cumulus  and 
stratus  types. 

In  1894  Clement  Ley  in  his  book 
Cloudland  ^vopo^^d  four  main  classes : 

1.  Radiation  clouds. 

2.  Interfret  clouds. 

3.  Inversion  clouds. 

4.  Inclination  clouds. 

Under  the  first  are  all  the  fog 
types;  under  the  second,  clouds 
caused  by  the  interaction  of  hori- 
zontal currents;  under  the  third, 
the  cumulus  clouds  or  clouds  caused 
by  condensation  due  to  vertical  cur- 
rents; and  under  the  fourth,  the 
cirrus  types. 

In  1889  Clayton  (an  American 
meteorologist  at  Blue  Hill  Observa- 
tory, whose  discussion  of  Cloud  Ob- 
servations in  the  Annals  of  Harvard 


OF  SAN  FRANCISCO  23 

Observatory,  Vol.    XXX,   Part   IV, 

1896,  is  the  best  that  we  know  of), 
prepared  a  classification  based  upon 
the  origin  of  the  cloud. 

1.  A  class  due  to  local,  nearly  vertical 
ascending  currents,  producing  the  clouds 
called  cumulus. 

2.  A  class  due  to  slow  obliquely  as- 
cending air.  To  this  belong  all  the  sheet 
clouds  of  stratification. 

3.  A  class  due  to  the  chilling  of  the 
lower  air  by  radiation  from  the  earth's 
surface.     To  this  class  belongs  the  fogs. 

4.  A  class  due  to  evaporation  of  the 
thinner  parts  of  clouds  already  formed, 
probably  caused  by  descent.  To  this 
class  belong  many  of  the  clouds  which 
appear  in  flocks  of  balls  or  rolls;  and 
certain  forms  of  cirrus. 

5.  A  class  of  clouds  due  to  differ- 
ences in  dire£^ion  and  velocity  of  the  air 
currents  at  different  levels.  To  this  class 
belong  the  cirrus. 

About  1890  an  International  class- 
ification was  agreed  upon  and  has 
been  for  years  in  general  use  among 


24       THE  CLOUDS  AND  FOGS 

meteorologists.  It  is  a  modification 
of  Howard's  system  and  is  hardly 
worthy  of  scientific  approval. 

Cirrus  or  feather  cloud.  This  is  the 
highest  cloud  and  moves  with  greatest 
velocity.  It  is  higher  in  summer  than  in 
winter.  Average  height  10  kilometers 
(6  miles). 

Cirro-stratus.  A  low  cirrus  and  less 
stable.  Solar  and  lunar  halos  are  due  to 
the  diffraction  of  light  through  these 
clouds. 

Cirro-cumulus.  Small  fleecy  clouds 
without  shadows  or  casting  faint  ones. 
They  are  arranged  in  broken  layers  and 
move  rapidly.  Average  elevation  6  to  10 
kilometers  (4  to  6  miles). 

Cumulus.  These  are  dense  clouds 
formed  chiefly  by  uprising  currents. 
When  the  cloud  is  opposite  the  sun  the 
surfaces  seen  by  the  observer  are  more 
brilliant  than  the  edges.  When  between 
the  sun  and  the  observer  the  cloud  throws 
a  strong  shadow.  Bases  are  often  flat 
and  mark  a  wide-spread  level  of  conden- 
sation. The  average  rate  of  motion  is 
9  meters  per  second  (20  miles  per  hour) 


OF  SAN  FRJNCISCO  25 

in   summer;    and  13  meters  per  second 
(30  miles  per  hourj  in  winter. 

Alto-cumulus.  Dense,  fleecy  clouds, 
grouped  in  flocks  or  rows.  These  are 
probably  formed  when  ascending  currents 
are  less  strong  than  in  the  case  of  cumulus  \ 
or  they  may  be  formed  by  mixture.  Their 
average  height  is  from  2  to  3  kilometers) 
(1  to  2  miles),  and  their  mean  velocity 
about  18  meters  (40  miles  per  hour)  per 
second. 

Cumulo-nimbus.  These  are  the  thun- 
derheads  and  shower  clouds.  Heavy 
masses  rising  like  mountains,  generally 
with  a  veil  of  cirrus  cloud  at  the  top,  the 
so-called  false  cirrus.  These  are  the 
largest  clouds  and  have  been  studied  more 
completely  than  any  other  type.  Some 
cumulo-nimbi  measured  by  Bigelow,  Kim- 
ball and  others  at  Washington,  show  the 
several  stages  of  formation,  namely,  the 
vapor,  liquid  and  solid  stadia.  In  one 
case  the  range  of  temperature  was  from 
2b°  C  (80°  F)  to  -59°  C  (-76  F) ;  or 
if  expressed  in  the  absolute  scale,  from 
299°A  to  214°A.  These  clouds  carry  a 
strong  ele£b-ical  charge  and  McAdie  has 
shown  that   there  are  marked  variations 


26       THE  CLOUDS  AND  FOGS 

in  the  electrical  potential  of  the  air, 
caused  by  the  approach  of  one  of  these 
cloud  masses. 

Stratus.  Lifted  fog,  or  sheet  cloud,  of 
low  elevation  and  without  special  struct- 
ure. Formed  by  the  mixing  of  air  strata 
at  different  temperatures  and  due  to  hori- 
zontal movement  of  the  air  rather  than 
rapid  upward  movement.  Average  ele- 
vation less  than  800  meters  (half  a  mile) , 
Average  velocity  7  meters  per  second  (15 
miles  per  hour) . 

Strato-cumulus.  Large  balls  or  rolls  of 
dark  cloud,  covering  the  sky,  especially 
in  winter.  Distinguished  from  nimbus 
by  the  rolled  form  and  absence  of  rain. 
Forms  at  a  moderate  elevation,  about 
2743  meters  (9,000  feet)  in  summer,  and 
somewhat  lower  in  winter  and  moves  at 
a  rate  of  about  11  meters  per  second  (25 
miles  per  hour) . 

Jlto  stratus.  A  thick  gray  or  bluish 
veil  showing  brighter  in  the  vicinity  of 
the  sun  and  moon  and  without  causing 
halos  may  produce  coronae.  The  aver- 
age height  is  about  5.5  kilometers  (3)^ 
miles)  in  summer;  and  5  kilometers  (3 
miles)  in  winter.     The  average  velocity 


OF  SAN  FRANCISCO  29 

is  18  to  22  meters  per  second   (40  to  50 
miles  per  hour) . 

Nimbus.  Rain  cloud.  Dark,  form- 
less clouds  with  ragged  edges  from  which 
generally  rain  or  snow  falls.  When  torn 
into  small  patches  it  is  called  scud  or 
fracto-nimhus. 

From  what  precedes  it  is  evident 
that  it  is  not  easy  to  positively  identify 
any  given  cloud.  Moreover  clouds 
of  the  low  levels  may  under  certain 
conditions  closely  resemble  clouds  of 
higher  levels.  Again  clouds  change 
form  so  rapidly  that  one  can  never 
be  sure  of  the  type. 

One  of  the  best  ways  to  keep  track 
of  the  various  types  and  their  proper 
levels  is  the  following  scheme : 

A.  Upper  clouds:  (a)  cirrus;  (b)  ctmh- 
stratus;  9,000  meters  or  29,500  feet. 

B.  Intermediate:  (a)  cirro-cumulus  and 
(b)  alto-cumulus;  3,000-7,000  meters  or 
11,500-23,000  feet. 

C.  Lower:  (a)  stratus-cumulus;  (b) 
nimbus;  2,000  meters  or  6,600  feet. 


30       THE  CLOUDS  AND  FOGS 

D.  Clouds  of  diurnal  ascending  cur- 
rents: (a)  cumulus;  top  1,800  meters, 
5,900  feet;  base  1,400  meters,  4,600 
feet;  (b)  cumulo-nimbus;  top  3,000-8,000 
meters,  9,800-26,000  feet;  base  1,400 
meters,  4,600  feet. 

E.  High  fogs:  (a)  stratus;  below  1,000 
meters,  3,280  feet. 

The  Munich  Conference  appointed 
a  Cloud  Commission  under  the  presi- 
dency of  Professor  Hildebrandsson 
to  prepare  an  International  Cloud 
Atlas.  This  was  published  in  Paris, 
1896,  by  Hildebrandsson,  Riggen- 
bach  and  Teisserence  de  Bort.  Some 
sixteen  types  of  clouds  are  given  with 
the  abbreviations  used  by  meteor- 
ologists.    They  are : 

Cirrus,  Ci. 
Cirro-stratus y  Ci.  S. 
Cirro-cumulus,  Ci.  Cu. 
Alto-cumulus,  A.  Cu. 
Alto-stratus,  A.  S, 
Strato-cumulus,  S.  Cu. 
Nimbus,  N. 


OF  SAN  FRANCISCO  3 1 

Cumulus,  C. 
Cumulo-nimbus,  Cu.  N. 
Stratus,  S. 

Fracto-cumulus,  Fr.  Cu. 
Fracto-nimhus,  Fr.  N. 
Fracto-stratus,  Fr.  S. 
Stratus-cumultformis,  S.  Cf. 
Nimhus-cumuliformis,  N.  Cf. 
Mammato-cumulus,  M.  Cu. 

Some  of  the  above  types,  especial- 
ly the  high  level  cumuli  and  the 
clouds  of  the  cumulo-nimbus  variety 
or  thunder-heads,  are  rare  in  San 
Francisco.  Cumuli^  when  they  do 
appear,  are  seen  mostly  on  the  east- 
ern horizon  and  are  in  general  con- 
nected with  thunderstorm  conditions 
in  the  Great  Valley  and  in  the  Sierra. 

Far  and  away  the  most  frequent 
cloud  formation  is  that  of  the  lower- 
most level,  from  sea  level  to  500  me- 
ters (1640  feet).  The  water  vapor 
is  condensed  at  temperatures  neither 
high  nor  low,  and  is  carried  in  from 
the  sea  with  the  prevailing  west  wind. 


CLOUD  MEASUREMENTS. 


[T  is  not  an  easy  matter  to 
measure  the  height  and 
velocity  of  a  cloud.  Ac- 
curate measurements  in- 
deed are  made  only  at  a 
few  of  the  leading  meteorological 
observatories. 

Of  several  methods  in  use,  the 
simplest  and  most  dired:  is  to  send 
up  hygrographs  on  kites  or  balloons 
and  follow  the  position  of  the  instru- 
ments with  a  theodolite.  When  the 
kites  enter  or  come  out  of  a  cloud 
the  height  can  be  determined  with 
considerable  accuracy  and  at  the  same 
time  the  variations  in  humidity,  pres- 
sure and  temperature  serve  to  further 
identify  and  establish  the  record.     A 

32 


OF  SJN  FRANCISCO  35 

second  way  is  to  follow  the  reflection 
of  a  cloud  in  a  nephoscope,  which 
is  a  black  mirror  provided  with  grad- 
uated circles  and  proper  index  arms. 
A  third  way  is  by  means  of  simul- 
taneous observations  with  alt-azimuth 
instruments.  Two  observers  at  a 
distance  connecSled  by  telephone  and 
knowing  accurately  the  intervening 
base  line  can  agree  upon  a  definite 
cloud  point  and  by  means  of  the 
vertical  and  horizontal  angles,  work 
out  the  cloud  height  and  velocity. 
Better  yet  are  cameras  mounted  on 
surveyors'  transits,  making  an  instru- 
ment known  as  a  photogrammeter. 
Where  observations  can  be  made 
from  mountain  observatories,  the 
upper  levels  of  the  fog  and  lower 
clouds  and  the  lower  levels  of  the 
intermediate  clouds  can  be  readily 
determined  by  diredt  comparison 
with  known  heights.  Thus  at  Mt. 
Tamalpais  it  is   an   easy  matter  to 


36       THE  CLOUDS  AND  FOGS 

obtain   the    heights    of    the    upper 
level  of  the  fog. 

Finally  the  heights  of  cloud  bases 
can  be  roughly  determined  from  a 
knowledge  of  temperature  decrease 
with  elevation  and  the  laws  of  con- 
densation governing  water  vapor  in 
free  air.  To  do  this  one  must  know 
the  temperature  at  different  levels 
and  the  probable  dew-point.  Dry 
air  cools  1°C.  each  hundred  meters 
of  ascent.  That  is,  dry  air  when 
ascending  and  expanding  normally 
and  without  receiving  heat  from  any 
outside  source,  will  cool  o.  55°F.  for 
each  hundred  feet.  But  such  a  con- 
dition rarely  exists.  Air  and  water 
vapor  rising  and  expanding  do  not 
cool  quite  so  rapidly.  The  formula 
used  is: 

1~  =  altitude  of  base  of  cloud. 

o.  78 

In  this  formula  db  is  the  temperature 
shown  by  the  dry  bulb  thermometer 


OF  SAN  FRANCISCO  37 

properly  exposed,  and  dp  is  the  dew- 
point. 

Few  scientific  investigations  are 
more  interesting  than  exadt  measure- 
ments of  the  clouds.  One  can  fol- 
low in  this  way  the  local  ascending 
currents,  the  formation  of  clouds, 
the  inclination  of  cloud  sheets  and 
in  brief  the  whole  circulation  from 
the  moment  evaporation  begins  until 
the  raindrop  or  snowflake  forms  and 
falls;  the  water  again  seeking  the 
broad  level  of  the  sea,  to  begin  its 
wandering  afresh. 


TRACKING  THE  CLOUDS- 


HERE  is  a  river  in  the 
ocean.  So  began  Mau- 
ry's famous  book,  the 
many  editioned  Physi- 
cal Geography.  He 
was  describing  the  Gulf  Stream  with 
its  fountain  in  the  Gulf  of  Mexico 
and  its  mouth  in  Ardic  seas;  and 
although  subsequent  study  and  dis- 
covery have  materially  modified  the 
original  conception  of  the  stream 
and  its  importance  in  controlling  the 
climate  of  England,  nevertheless  the 
tracking  of  an  individual  current  in 
the  great  spread  of  Atlantic  waters 
was  an  achievement  worthy  the 
recognition  it  received  from  the 
nations.     There  are  other  rivers  in 

38 


CiRRO-cuMUu  (1).     Compare  imth  plaU  beloiu. 


CiRRO-cuMUU  (2).     One  minuU  change. 


OF  SAN  FRANCISCO  41 

the  seas.  In  the  Atlantic  no  less 
than  twelve  well  marked  currents 
and  drifts  are  now  charted;  and  in 
the  Pacific  at  least  ten.  The  best 
known  of  the  Pacific  currents  are 
the  Kuroshiwo  or  Japan  current, 
passing  partly  into  the  Sea  of  Japan, 
but  mostly  washing  the  southeast 
coast  of  the  Islands  and  then  drift- 
ing eastward;  the  California  current 
which  flows  from  the  North  Pacific 
southeast,  south  and  then  southwest, 
becoming  finally  a  westerly  drift; 
and  the  North  Equatorial  current 
which  under  the  influence  of  the 
Trade  Winds  flows  westward  with  a 
velocity  of  ten  or  more  miles  per 
day  from  the  Central  American 
coast,  recurving  gradually,  north- 
ward, as  it  reaches  the  Philippines. 

But  if  there  are  many  rivers  in 
the  sea,  there  are  more  rivers  in  the 
larger  ocean,  the  atmosphere.  In 
fad:  the  great  water  currents  are  set 


42       THE  CLOUDS  AND  FOGS 

in  motion  and  driven  in  large  de- 
gree by  the  currents  of  air.  Certain 
winds,  such  as  the  Trades,  the  Coun- 
ter Trades,  the  Prevailing  Westerlies, 
and  Roaring  Forties  (referring  to 
the  winds  rather  than  the  latitudes), 
are  well  known.  Meteorologists 
have  been  busy  for  many  years 
sounding  the  ocean  of  air  and 
charting  the  main  streams  and  drifts. 
But  even  more  than  this,  is  the 
determination  of  temperatures,  pres- 
sures, humidities,  wind  velocities  and 
the  flow  of  the  air  at  all  levels  from 
the  ground  up  to  the  level  of  the 
highest  clouds.  In  studying  the 
currents  of  the  sea,  men  are  con- 
cerned chiefly  with  surface  move- 
ments; but  in  aerial  work  we  must 
know  not  only  the  movements  near 
the  ground  and  in  a  horizontal 
direction,  but  all  the  uprising  and 
descending  currents.  Charts  of  the 
atmosphere  are  now  published;  and 


OF  SJN  FRANCISCO  43 

in  such  a  book  as  the  one  issued  this 
year,  1911,  by  Professors  Rotch  and 
Palmer,  aviators  and  aeronauts  can 
find  for  their  guidance,  the  prevail- 
ing conditions  at  various  levels.  For 
example,  the  wind  velocity  increases 
with  height  and  the  increase  is 
greater  in  winter  than  in  summer; 
but  during  the  late  spring  and  eariy 
autumn  the  increase  between  500 
meters  (1640  feet)  and  1500  meters 
(4921  feet)  is  very  gradual.  Again, 
the  sea  breeze  is  found  to  be  a  shal- 
low stream  while  winds  from  the 
same  direction,  but  of  cyclonic 
origin,  are  of  considerable  depth. 
Winter  winds  are  stronger  than 
summer  winds  at  neariy  all  levels, 
and  westeriy  winds  stronger  than 
easteriy  winds. 

The  possibility  of  utilizing  the 
great  rivers  of  the  atmosphere  in 
aerial  navigation  naturally  suggests 
itself.     Indeed  the  problem  of  using 


44       THE  CLOUDS  AND  FOGS 

the  Trade  Winds  for  passages  from 
Europe  to  America  has  been  dis- 
cussed ;  and  while  practicable,  it  has 
been  pointed  out  by  Professor  Rotch 
that  to  make  the  return  advantageous- 
ly one  would  have  to  rise  above  the 
Counter  Trades,  owing  to  their  irreg- 
ularity, and  utilize  the  eastward  drift 
in  the  cirrus  level.  This  can  be 
done  and  in  the  future  may  be 
accomplished,  but  at  present  both 
for  comfort  and  safety  another  route 
which  however  is  far  north,  will 
have  to  be  taken. 

Over  the  Pacific,  air  lanes  of  travel 
have  not  yet  been  charted  with  any 
great  detail.  Leaving  the  Asiatic 
coast  the  lower  winds  during  many 
months  would  carry  the  traveller  to 
Alaska;  but  the  strong  northwest 
winds  of  summer  could  be  used  to 
come  south.  The  return  trip  could 
best  be  made  by  leaving  the  Ameri- 
can  coast  south   of   California  and 


OF  SAN  FRANCISCO  47 

utilizing  the  northeast  Trades.  If 
cloud  masses  were  as  permanent  and 
substantial  as  air  ships  we  should 
have  had  long  before  this  a  better 
knowledge  of  the  currents  of  the 
atmosphere.  But  because  they  form 
and  dissolve  so  rapidly  and  incessant- 
ly and  can  not  long  be  identified, 
meteorologists  have  found  it  a  diffi- 
cult matter  to  determine  true  air 
motion  by  study  of  the  clouds. 


THE  FOGS. 


OG  is  San  Francisco*  s great- 
est asset.  This  sounds 
quixotic,  but  the  state- 
ment is  nevertheless  true. 
For  while  fog  is  an  adlive 
and  permanent  menace  to  naviga- 
tion, a  source  of  uncertainty  and 
delay  and  worry  to  travellers,  and 
carries  a  chill  that  goes  to  the  very 
marrow  of  thinly-clad  summer  tour- 
ists, nevertheless  it  keeps  the  city 
cool  in  summer  and  thus  makes  for 
health;  also  it  keeps  the  city  warm 
in  winter,  preventing  frosts  and 
moderating  the  fall  in  temperature. 
The  lowest  recorded  temperature  at 
San  Francisco  is  -2°C.  (29°F.),  and 
the  highest    38°C.    (lOl^F.)     The 

48 


OF  SAN  FRANCISCO  49 

mean  temperature  is  13°C.  (S6°F.) 
San  Franciscans  love  their  fog.  When 
away  from  the  city  they  pine  for  it, 
and  especially  during  summer.  Not 
without  reason  do  they  appreciate 
the  cooling  effed:  of  the  fog.  It 
enables  one  to  sleep  through  summer 
nights  and  rise  refreshed  and  ready 
for  the  day's  requirements. 

Owing  to  the  peculiar  topography 
of  the  San  Francisco  Bay  sedtion,  the 
prevailing  westerly  winds  (sometimes 
erroneously  called  Trades)  have  their 
velocity  increased  near  the  Golden 
Gate.  There  are  certain  well-marked 
stream  lines  in  the  general  current 
from  west  to  east,  and  in  these  streams 
large  quantities  of  the  condensed 
water  vapor  lying  beyond  the  heads 
and  along  the  coast,  are  carried  in 
through  the  Gate,  at  heights  varying 
from  sea  level  to  500  meters  (1640 
(feet).  There  are  times  when  the 
formation  of  the  fog  is  purely  local 


N 


50       THE  CLOUDS  JND  FOGS 

and  the  area  covered  small;  but  there 
are  also  times  when  a  bank  of  fog 
will  extend  along  the  coast  2000 
kilometers  (1244  miles). 

In  general  the  fog  hugs  the  coast 
and  is  most  dense  a  short  distance 
from  the  shore  line;  but  occasionally 
it  will  cover  the  sea  for  hundreds  of 
miles  and  be  reported  by  steamers 
several  days  out  from  port. 


Changing  Alto-cumuu  (1).     Compare  tmth  plate  belonxj. 


Changing  Alto-cumuli  (2).     One  minute  later. 


TYPES  OF  FOG, 


IN  the  vicinity  of  San 
Francisco  there  are  sev- 
eral well-marked  types 
of  fog.  First  and  most 
prominent  is  the  sum- 
mer afternoon  sea  fog  which  forms 
not  far  west  of  the  Gate,  and  at  times 
within  the  Gate,  on  the  Sausalito 
hills  and  south  slopes  of  Tamalpais, 
and  moves  inland  at  an  average  rate 
of  7  meters  per  second,  16  miles  per 
hour.  The  second  type  is  the  tule 
fog,  named  from  the  tules  or  bul- 
rushes in  the  Sacramento-Joaquin 
river  beds.  This  is  a  low-lying, 
dense  land  or  river  fog,  which  forms 
during  winter  mornings  and  drains 
slowly  seaward,    half    a   meter   per 

53 


54       THE  CLOUDS  AND  FOGS 

second  or  a  mile  an  hour.  It  is 
essentially  a  valley  fog  and  is  most 
marked  in  the  lowlands;  but  some- 
times on  clear  winter  nights  when 
thecoolingdue  to  radiation  is  marked, 
fog  forms  early  over  the  city  and  bay, 
dissipating  before  noon.  As  a  rule 
the  city  hills  and  even  the  roofs  of 
the  tall  office  buildings  are  above  the 
fog.  "Although  there  are  certain  as- 
censional movements,  the  high  parts 
of  the  city  are  generally  out  of  the 
fog  several  hours  before  the  low 
portions. 

The  third  type  is  a  nondescript 
fog,  formed  by  a  mixture  of  city 
smoke  and  dust  with  the  condensed 
vapor.  This  lies  about  200  meters, 
or  650  feet,  above  the  city  streets. 
A  pall  of  smoke  and  fog  drifts  slowly 
seaward  during  the  morning  hours, 
especially  in  the  spring  and  autumn, 
and  returns  again  about  one  p.m., 
driven  in  by  the  west  wind.     In  such 


OF  SAN  FRANCISCO  55 

cases  it  appears  as  a  dark,  low  cloud 
and  for  a  period  of  fifteen  minutes 
or  half  an  hour  causes  a  noticeable 
darkness. 

At  Mt.  Tamalpais  one  may  look 
down  upon  the  fog  and  note  the 
various  stream  lines.  There  are 
marked  differences  in  temperature, 
humidity  and  air  motion  within 
comparatively  short  distances  both 
in  a  horizontal  and  vertical  direct- 
ion. The  whole  Bay  sedtion  is 
remarkable  and  may  indeed  be 
considered  as  a  magnificent  natural 
laboratory  in  which  experiments 
bearing  upon  the  cloudy  condensa- 
tion of  water  vapor  are  wrought 
daily.  Ocean,  bay,  mountain  and 
foothill  lie  in  close  juxtaposition. 
A  valley  level  as  a  table  is  connected 
with  the  ocean  by  a  narrow  water 
passage,  while  on  either  side  are  hills 
reaching  in  some  cases  above  the 
1000  meter  (3280  feet)  level. 


56       THE  CLOUDS  AND  FOGS 

In  summer  the  afternoon  sea  fog 
varies  in  depth  from  30  meters  (100 
feet)  to  500  meters  (1640  feet),  the 
depth  decreasing  as  the  distance  in- 
land increases.  On  summer  after- 
noons the  velocity  of  the  wind  at 
San  Francisco  rises  with  almost 
clock-like  regularity  to  about  10 
meters  per  second  or  22  miles  per 
hour,  and  a  solid  wall  of  fog  comes 
through  the  Golden  Gate,  causing 
a  fall  in  temperature  to  13°C.(55°F.) 
which  is  approximately  the  tempera- 
ture of  the  surface  water  of  the  sea 
in  this  latitude.  The  upper  level  of 
the  fog  can  be  plainly  seen  from  the 
high  hills  in  the  vicinity.  Moreover 
above  the  fog  level  the  air  is  cloud- 
less and  the  temperature  is  often  as 
highas33X.  (90°F.) 

The  Pacific  fogs  are  different  from 
the  fogs  of  the  North  Atlantic,  for 
the  latter  occur  irregularly,  although 
in  certain  localities  persistently,  and 


OF  SJN  FRANCISCO  59 

are  due  probably  to  thin  strata  of 
warm  moist  air  passing  over  cold 
water  surfaces.  On  the  other  hand 
our  Pacific  fogs  are  more  probably 
due  to  the  mixture  of  two  air  streams, 
one  warm  and  the  other  not  so  warm, 
but  heavily  laden  with  water  vapor. 
The  moisture  of  the  lower  current  is 
cooled  by  a  slight  upUfting  and  ex- 
pansion; but  above  a  certain  limit 
no  fog  forms  owing  to  the  warmer 
air  stream  moving  slowly  seaward 
or  in  an  opposite  direction  from  the 
lower  fog-laden  current.  The  sup- 
ply of  water  vapor  comes  from  the 
sea  and  there  is  probably  some  direct 
connection  between  the  steady  and 
strong  northwest  winds  and  the  di- 
rection and  force  of  the  ocean  cur- 
rents in  this  section.  Both  the  air 
and  water  isotherms  bend  sharply 
southward  in  the  latitude  of  40° 
north  and  longitude  130°  west.  The 
water  is  somewhat  warmer  than  the 


60       7 HE  CLOUDS  AND  FOGS 

air.  It  must  be  remembered,  how- 
ever, that  the  air  temperature  is  that 
of  the  lowermost  level  and  does  not 
correctly  indicate  the  true  tempera- 
ture of  the  general  air  mass.  One 
would  naturally  anticipate  that  the 
water  would  be  colder  than  the  air 
since  both  move  from  the  north  and 
water  has  a  higher  specific  heat. 

Cooling  is  necessary  to  produce 
condensation  and  this  may  be  accom- 
plished by  an  uplifting  of  the  air 
mass  with  resulting  expansion  and 
work  done  against  pressure  at  a  given 
level,  or  by  the  radiation  and  loss  of 
heat  when  the  upper  air  is  dry,  dust- 
free  and  vapor-free,  or  finally  by 
mixture  with  cold  air. 

As  yet  very  little  is  known  about  the 
nuclei  which  serve  as  centers  of  con- 
densation, and  until  this  phase  of  the 
problem  is  investigated,  we  cannot 
speak  definitely  concerning  the  origin 
of  fog. 


SUNSHINE  AND  FOG. 

OMPARING  San  Fran- 
cisco with  other  cities  in 
the  United  States,  it  must 
be  admitted  that  the 
amount  of  sunshine  re- 
ceived is  not  as  large  as  it  ought  to 
be.  Nevertheless  the  city  receives 
a  larger  amount  than  the  general 
prevalence  of  sea  fogs  vv^ould  lead 
one  to  believe.  An  interesting  com- 
parison is  that  of  San  Francisco  and 
Baltimore,  the  latter  a  coast  city 
slightly  farther  north,  however,  than 
San  Francisco.  We  find  that  the 
mean  percentage  of  possible  sunshine 
at  Baltimore  for  the  month  of  Janu- 
ary is  50  per  cent,  and  at  San  Fran- 
cisco 46  per  cent. ;   for  February  at 

61 


62       THE  CLOUDS  AND  FOGS 

Baltimore  59  per  cent,  and  at  San 
Francisco  52  per  cent. ;  for  March  at 
Baltimore  57  per  cent,  and  San  Fran- 
cisco 56  per  cent.  It  therefore  ap- 
pears that  during  the  first  three 
months  of  the  year  there  is  more 
sunshine  in  Baltimore  than  in  San 
Francisco.  During  April,  May  and 
June,  however,  San  Francisco  has 
more  sunshine,  as  shown  by  the 
following  table : 

j^pril —  Baltimore  60  per  cent. 

San  Francisco  67  per  cent 
May  —  Baltimore  54  per  cent. 

San  Francisco  64  per  cent. 
June  —  Baltimore  62  per  cent. 

San  Francisco  84  per  cent. 

The  effect  of  the  summer  fogs  in 
reducing  the  amount  of  sunshine  at 
San  Francisco  is  strikingly  shown  by 
the  records  for  the  months  of  July 
and  August.  Attention  is  called  to 
the  table    (page   67),  showing  the 


i 


OF  SAN  FRANCISCO  65 

effect  of  the  fog  between  7  a.m.  and 
9:30  a.m.;  and  6  p.m.  and  8  p.m. 
during  July,  August  and  September. 

For  July  the  average  percentage  of 
sunshine  at  Baltimore  is  63  per  cent, 
and  at  San  Francisco  65  per  cent. ; 
for  August  at  Baltimore  61  per  cent, 
and  at  San  Francisco  58  per  cent.; 
for  September  at  Baltimore  67  per 
cent.,  San  Francisco  65  per  cent.; 
for  October  at  Baltimore  60  per  cent. 
San  Francisco  67  per  cent. ;  for  No- 
vember at  Baltimore  50  per  cent.; 
San  Francisco  S7  per  cent. ;  for  De- 
cember at  Baltimore  51  per  cent,  and 
at  San  Francisco  55  per  cent. 

It  is  thus  seen  that  during  the 
months  of  October  November  and 
December  there  is  a  higher  percent- 
age of  the  possible  sunshine  at  San 
Francisco.  For  the  year  the  average 
percentage  of  possible  sunshine  at 
Baltimore  is  58  per  cent,  and  at  San 
Francisco  60  per  cent.     The  figures 


66       THE  CLOUDS  AND  FOGS 

for  Baltimore  are  taken  from  Dr. 
Fassig's  report  on  the  Climatology 
of  Maryland. 

If  we  compare  San  Francisco  with 
other  large  American  cities,  we  find 
there  were  in  a  given  year: 

2729  hours  of  sunshine  at  New  York. 
2423  hours  of  sunshine  at  Chicago. 
2548  hours  of  sunshine  at  Philadelphia. 
2763  hours  of  sunshine  at  Boston. 
2263  hours  of  sunshine  at  St.  Louis. 
2266  hours  of  sunshine  at  Pittsburg. 
2869  hours  of  sunshine  at  San  Francisco. 

These  data  are  from  the  last  An- 
nual Report  of  the  Chief  of  the 
Weather  Bureau. 


OF  SAN  FRANCISCO 


67 


Percentage  of  Sunshine  at  Mt.  Tamalpais 

13  Years'  Records  to  1910-11. 


5 

A.  M. 


6 
A.  M. 


7 

1A.M. 


8 

A.M. 


9 
A.  M 


10 

A.  M. 


11 

A.M. 


M. 


January. . . 
February. . 

March 

April 

May 

June 

July 

August 

September. 
October... 
November. 
December. 


42 
48 
52 
70 
76 
86 
92 
88 
82 
71 
50 
56 


53 
58 
59 
77 
82 
91 
96 
93 
97 
80 
62 


54 
57 
58 
76 
83 
91 
96 
94 
88 
80 
64 
68 


1 

[P.M. 


2 

p.  M 


3 

4 

P.M. 

p.  M. 

51 

46 

58 

55 

63 

59 

80 

79 

86 

86 

95 

94 

98 

98 

97 

97 

90 

90 

81 

78 

64 

59 

64 

53 

5 

P.M. 


6 

[P.M. 


7 

[p.  M. 


8 

IP.  M. 


January 

February 

March 

April 

May 

June 

July 

August 

September 

October 

November 

December 


52 
61 
64 
80 
86 
95 
98 
96 
90 
81 
65 
62 


40 
49 
55 
77 
84 
94 
97 
96 
87 
82 
52 


43 
63 
70 

87 
93 
92 
85 


67 
82 
93 
91 


68       THE  CLOUDS  AND  FOGS 

Percentage  of  Sunshine  at  San  Francisco 

18  Years'  Records  to  1910-11. 


5 

A.M. 


6 

A.M. 


7 

A.M. 


8 

A.M. 


9 

A.M. 


10 

A.M. 


11 
A.M. 


M. 


January. . . 
February. . 

March 

April 

May 

June 

July 

August 

September. 
October. . . 
November. 
December. 


33 
42 
29 


16 
33 
38 
42 
24 
17 
28 


28 
29 
41 
48 
53 
32 
21 
34 
34 
29 


22 
24 
36 
52 
54 
63 
41 
28 
44 
43 
30 
30 


33 
40 
49 
65 
65 
73 
55 
39 
57 
55 
43 
42 


48 
53 
60 
74 
74 
84 
71 
58 
69 
67 
56 
56 


57 
60 
69 
79 
81 
90 
86 
77 
79 
78 
67 
65 


61 
67 
71 
83 
85 
93 
93 


83 
73 


1 

p.  M. 


2 

p.  M. 


3 

p.  M. 


4 

P.M. 


5 

P.M. 


6 

IP.  M. 


7 

P.M. 


8 

P.M. 


January 

February 

March 

April 

May 

June 

July 

August 

September. . 

October 

November 

December.. . 


64 
69 
75 
85 
86 
94 
97 
93 
90 
87 
76 
70 


64 
71 
75 

84 
88 
95 
97 
96 
90 
88 
76 
67 


61 
68 
74 
83 
85 
95 
97 
95 
89 
85 
72 
64 


49 
64 
88 
79 
81 
94 
93 
85 
80 
79 
61 
51 


36 
51 
60 
70 
72 
86 
82 
71 
68 
61 
42 
36 


30 
34 
42 
59 
58 
72 
61 
44 
54 
48 


36 
48 
45 
62 
43 
31 
42 


37 
53 
42 
31 


THE  FOG  CURTAIN  AND 

THE  SUN. 

VERY  minute  of  sunshine 
has  been  recorded  for  the 
past  thirteen  years  at  Mt. 
Tamalpais.  And  as  the 
same  has  been  done  at 
San  Francisco,  but  for  even  a  longer 
period,  we  are  able  to  say  with  some 
certainty  how  much  sunlight  is  shut 
out  from  the  lower  station  by  the 
curtain  of  fog,  since  during  most  of 
the  year  the  curtain  is  drawn  below 
the  level  of  the  summit. 

In  an  average  year  the  total  num- 
ber of  hours  of  bright  sunshine  at 
San  Francisco  will  be  about  2900. 
Above  the  fog  curtain,  say  at  a  height 
of  two  thousand  feet,  there  would  be 

71 


72       THE  CLOUDS  AND  FOGS 

about  3400  hours.  Therefore  the 
curtain  shuts  out  about  15  per  cent, 
of  the  possible  sunlight.  And  this 
screening  takes  place  chiefly  in  the 
morning  and  evening  hours  when 
indeed  the  sunlight  is  most  welcome. 
We  could  better  spare  the  sunlight 
in  the  noonday  hours.  However, 
in  midsummer,  the  fogs  do  material- 
ly temper  the  heat  and  diminish  the 
glare.  In  August  the  city  receives 
but  68  per  cent,  of  the  possible  sun- 
shine, while  the  mountain  receives 
80  per  cent.,  and  in  some  years  100 
per  cent,  of  the  possible  amount. 

Once  in  a  while  the  city  receives 
more  sunshine  than  the  mountain 
does.  This  is  apt  to  occur  during 
March  or  some  of  the  winter  months. 
At  such  times  clouds  form  on  the 
mountain  crest  and  remain  there; 
but  in  the  valleys  and  at  sea  level 
there  is  bright  sunshine. 


FOG  AND  EQUIVALENT 
RAIN. 

[ATCHING  the  fog  masses 
pour  through  the  Gate, 
the  question  naturally 
arises:  ** Could  this  vapor 
be  condensed;  and  if  so 
how  much  rain  would  result?"  Fog 
can  be  dissipated  by  electrical  agen- 
cies and  the  experiments  of  Lodge 
and  others  are  fascinating  and  point 
a  way  toward  the  eventual  control  of 
fog.  But  at  the  present  time  fog 
dissipation  on  a  commercial  scale 
has  not  been  attempted.  The  ex- 
periments of  a  Californian,  Dr.  Cot- 
trell,  in  smoke  deposition  and  his 
successful  removal  of  poisonous  gases 
in  smelter  fumes,  offer  perhaps  the 

73 


74       THE  CLOUDS  AND  FOGS 

first  approach  to  commercial  clarify- 
ing of  the  atmosphere. 

As  to  the  water  content  of  a  given 
fog  mass :  on  an  ordinary  foggy  after- 
noon in  mid-summer,  probably  not 
less  than  a  million  tons  of  water  are 
carried  each  hour  inland,  over  a  line 
drawn  from  Point  Lobos  to  Point 
Bonita.  If  this  vapor  could  be  con- 
densed and  all  fall  as  rain,  which 
however  would  not  be  a  simple  pro- 
cess, there  would  be  on  each  acre 
about  0.14  inch  of  water. 

As  a  matter  of  fad:,  on  very  moist 
nights,  or  when  supersaturation  oc- 
curs, we  find  about  0.02  inch  of 
water  in  the  rain  gage,  in  twelve 
hours.  It  is  plain  then  that  nearly 
all  the  visible  vapor  or  fog  is  car- 
ried inland,  and  as  the  temperature  I 
rises  becomes  invisible  and  acts  just  \ 
like  a  dry  gas.  But  in  its  eastern 
march  it  rises,  and  rising  expands 
and  cools.     If  the  cooling  is  rapid 


OF  SAN  FRANCISCO  77 

the  clouds  form;  and  thus  we  find 
as  it  were,  a  second  birth  of  the  cloud 
form  and  recognize  in  the  curling 
wisps  of  white  above  the  Sierra  the 
same  vapor  that  in  an  earlier  exis- 
tence we  knew  as  sombre  fog. 


PAST  AND  FUTURE  OF 
THE  FOG. 


RE  yet  our  English  Bible 
had  been  translated  and 
before  Shakespeare  had 
learned  his  letters,  the 
first  visitors  to  our  shores 
bitterly  abused  our  climate.  And 
they  came  in  June,  too.  The  crew 
of  the  Golden  Hinde,  who  left  Ply- 
mouth forty  years  before  the  Pilgrim 
Fathers  and  spent  nearly  a  month 
near  Point  Reyes  Light,  said  some 
exceedingly  harsh  things  about  our 
weather  and  particularly  of  the  fog. 
According  to  the  Chaplain,  these 
first  globe-encirclers  did  not  '4n  the 
whole  fourteene  days  together  find 
the  air  so  clear  to  be  able  to  take  the 

78 


OF  SAN  FRJNCISCO  79 

height  of  sunne  or  starre."  The 
mildest  terms  used  in  describing  the 
fog  were : 

**Most  vile,  thick  and  impenetrable." 

Little  did  they  know  that  the  same 
fog  shut  them  out  from  the  Bay  of 
San  Francisco.  They  had  passed 
north  of  it  and  rather  far  out,  but 
even  when  they  left  and  sailed  south- 
west within  twenty  miles  of  the  Gate, 
they  knew  nothing  of  it.  Full  of 
wonder  as  the  trip  had  been,  when 
they  got  back  to  England  they  could 
not  tell  of  a  glorious  stretch  of  inland 
water,  fog  wrapped  it  is  true  at  the 
western  end,  but  sunlit  within  and 
beyond  the  reaching  of  the  fog. 
The  union  of  lordly  rivers,  the  broad 
fields  of  a  great  valley  quivering  in 
the  summer  heat,  the  mighty  trees 
and  snow  clad  peaks  remained  undis- 
covered. The  fog  hid  from  their 
view  the  gateway  to  a  delectable  land ; 


80       THE  CLOUDS  AND  FOGS 

and  Drake  who  formally  and  with 
some  show  took  over  the  sovereignty 
of  the  land,  never  dreamed  that  in 
his  voyage  round  the  world  he  missed 
an  empire  through  a  veil  of  fog. 
Within  five  hours  sail  from  where 
he  careened  his  little  ship  he  and  his 
shivering  men  could  have  basked  in 
sunshine  and  enjoyed  the  warmth 
of  perfedt  June  days.  How  they 
would  have  marvelled  at  the  change, 
for  many  marvel  now  at  the  marked 
transition  from  cold  to  warmth. 

If  some  prophetic  dreamer  in  the 
crew  had  told  these  rough  men  that 
in  eight  generations  men  of  flesh  and 
blood  like  themselves,  speaking  the 
same  mother  tongue,  were  to  sail 
these  waters  in  iron  ships,  by  har- 
nessing the  expansive  power  of  water 
vapor — nay,  more,  that  because  of 
their  steam  engines  they  could  sail 
at  will  and  neither  wind  nor  wave 
bar  their  progress,  then  these  bluff 


OF  SAN  FRJNCISCO  83 

marinersin  leather  jerkins  would  have 
laughed  uproariously  and  howled 
aloud  their  derision. 

And  are  not  we  today  somewhat 
like  the  crew  of  the  Golden  Hinde 
in  that  we  do  not  see  beyond  the 
veil  of  the  immediate  present  and 
dream  not  of  the  possibilities  of  the 
future?  There  is  more  to  a  bank  of 
fog  than  the  accidental  grouping  of 
little  globules  of  condensed  water 
vapor.  There  is  a  reason  for  the 
massing  and  there  are  processes  at 
work  which  if  understood  and  mas- 
tered would  lead  to  marvellous 
achievement.  It  is  as  difficult  for 
us  to  conceive  of  future  methods  of 
communication  and  transportation 
as  it  was  for  the  sailors  of  Drake's 
age  to  imagine  a  steam  driven  ship. 

Looking  at  the  fog  masses  as  they 
silently  spring  into  being  and  again 
as  silently  disappear,  one  wonders 
at    the    forces    involved.     Back    of 


84       THE  CLOUDS  AND  FOGS 

condensation  is  nucleation  and  back 
of  that  ionization.  Each  atom  holds 
a  number  of  electrical  particles  each 
of  which  in  turn  carries  a  certain 
eledtrostatic  charge.  There  are  posi- 
tive ions  and  negative  ions,  the  for- 
mer having  lost  electrons  and  the 
latter  having  gained.  The  mechan- 
ical activity  of  the  smallest  negative 
ion  is  greater  than  that  of  the  smallest 
positive.  In  some  way  not  now 
clearly  understood  potential  gradients 
rise  rapidly  in  a  cloud  mass  and  there 
are  differences  of  potential  amount- 
ing to  several  hundred  volts  within 
a  foot  or  two.  Who  that  has  ever 
seen  the  lightning  play  during  a 
thunderstorm  has  not  wondered  at 
the  apparently  endless  supply  and 
waste  of  energy?  An  intense  flash 
represents  the  using  up  of  10,000 
kilowatts  per  second.  In  other  words 
seven  million  foot  pounds  of  energy. 
This  is  a   large   quantity  from    an 


OF  SJN  FRJNCISCO  85 

electrical  standpoint;  but  when  ex- 
pressed in  terms  representing  heat 
energy  it  is  not  much  more  than  the 
latent  heat  of  evaporation  or  conden- 
sation of  ten  pounds  of  water.  Think 
then  of  how  much  equivalent  elect- 
rical energy  there  may  be  in  the 
making  of  an  ordinary  fog  bank! 
When  shall  we  know  enough  to 
utilize  this  energy?  One  of  the 
brightest  of  American  electricians, 
Steinmetz,  has  likened  the  discharge 
of  a  cloud  to  a  landslide,  which  sets 
off  a  series  of  landslides.  He  asks 
us  to  imagine 

"...  a  relief  map  built  of  wet  sand, 
the  hills  representing  the  dense  por- 
tion of  the  cloud  or  the  places  of  high 
potential,  and  the  valleys  the  light  or 
low  potential  places.  Then  where 
the  declivity  is  very  steep  a  slide  oc- 
curs which  causes  another  slide  and 
so  on,  until  the  hills  are  levelled  and 
the  valleys  filled,  or  in  other  words 
the  electric  potential  is  equalized." 


86       THE  CLOUDS  AND  FOGS 

Another  physicist*  has  thrown  light 
upon  the  coUision  of  ions  with 
atoms  and  shows  how  ionization 
proceeds  by  geometric  progression. 
In  the  air  close  to  a  wire  carrying  a 
current  of  electricity  of  very  high 
potential,  such  as  some  of  our  high 
transmission  lines  in  California,  there 
is  collision  of  the  atoms  and  faint 
luminosity  which  is  of  course  best 
seen  at  night.  This  is  the  probable 
cause  of  the  corona  or  faint  bluish 
light  seen  at  night  on  high  tension 
electrical  conductors.  As  for  the 
fog,  meteorologists  hope  to  be  able 
to  trace  the  real  beginning  of  nucle- 
ation,  haziness  and  condensation  in 
the  play  of  the  ions  and  electrons. 
Then  will  the  sombre  masses  of  water 
vapor  that  move  overhead  and  dim 
the  brightness  of  the  sun  take  on  a 
new  significance,  and  in  the  fog  men 
will  read  a  wonder  tale  of  forces  now 
all  unknown  and  unmeasured. 

♦Professor  Harris  J.  Ryan,  of  Stanford  University 


SIXTY-TWO  YEARS  OF 
RAINFALL. 

|N  no  portion  of  the  habi- 
table globe  are  seasonal 
rainfalls  more  closely 
watched  and  studied  than 
in  California.  There  are 
many  sedions  of  the  United  States 
where  departures  from  normal  con- 
ditions are  followed  with  interest; 
but  there  is  no  district  where  an 
excess  or  deficiency  in  rainfall  means 
more  or  is  more  diredtly  and  vitally 
conned:ed  with  the  welfare  of  the 
community  than  in  our  own  State. 
The  history  of  each  year's  rainfall 
is  written  in  the  crop  yield  and  in 
our  material  prosperity.  If  rain  falls 
in  sufficient  amount  within  seasonal 

89 


90       THE  CLOUDS  AND  FOGS 

limits  and  is  well  distributed  as  to 
time  and  amount,  a  good  year  based 
upon  abundant  crop  yield  may  be 
anticipated.  On  the  other  hand, 
scanty  rainfall,  or  even  an  average 
rainfall  badly  distributed  means  poor 
harvests  and  their  consequences.  As 
agriculture  underlies  commercial 
prosperity,  it  is  plain  that  the  adliv- 
ities  and  industries  of  the  State  are 
bound  up  with  and  directly  depend- 
ent upon  the  seasonal  rainfall  and 
the  resulting  supply  of  water. 

Not  without  reason  then  do  our 
people  at  the  beginning  of  each  rainy 
season  take  an  interest  in  the  fre- 
quency and  intensity  of  the  rains 
and  try  to  forecast  the  character  of 
the  impending  season. 

The  accompanying  diagrams  of 
seasonal  rainfall  (page  101)  first  came 
into  prominence  during  a  period  of 
drought,  the  dry  seasons  of  1897-98 
and    1898-99,    when    there    was    a 


OF  SAN  FRANCISCO  91 

widespread  uneasiness  and  general 
misapprehension  that  the  climate  was 
permanently  changing.  The  charts 
show  conclusively  that  such  periods 
are  only  incidental  and  no  true  indi- 
cation of  a  permanent  change. 

It  is  plain  that  there  is  no  regular 
sequence  of  wet  and  dry  seasons,  and 
this  is  as  it  should  be,  because  while 
law  is  supreme  in  meteorology  and 
our  storms  develop,  move  and  dis- 
appear in  accordance  with  physical 
laws,  understood  in  part,  there  are 
too  many  independent  variables  en- 
tering into  the  problem  of  rain  for- 
mation and  the  condensation  of  the 
water  vapor  of  the  air  to  allow  us  to 
hope  for  a  regular  and  easy  solution 
of  the  problem.  An  abnormally  wet 
month  is  not  necessarily  followed  by 
another  of  the  same  character.  No 
one  can  predict  from  the  existence 
of  one  dry  month  in  winter  that  the 
balance  of  the  season  will  be  dry. 


92       THE  CLOUDS  AND  FOGS 

All  that  we  can  say  at  present  is  that 
wet  seasons  and  dry  seasons  come 
and  go  in  a  very  irregular  way.  Nor 
is  there  any  determinable  period 
between  abnormal  conditions.  The 
chart  herewith  covers  the  rainfall 
for  sixty-two  years  at  San  Francisco. 
If  we  divide  the  period  into  decades, 
we  have: 

SAN   FRANCISCO. 
SEASONS.  INCHES. 

10  seasons,  1849-1859:  5778  mm.  or  227.47 
10  seasons,  1859-1869:  6549  mm.  or  257.85 
10  seasons,  1869-1879:  5766  mm.  or  227.00 
10  seasons,  1879-1889:  5950  mm.  or  234.23 
10  seasons,  1889-1899:  5558  mm.  or  218.81 
10  seasons,  1899-1909:  5341mm.  or  210.28 

The  mean  seasonal  rainfall  is 
S83mm.  or  22.90  inches. 

It  is  interesting  to  note  that  dur- 
ing the  month  of  January,  1862, 
more  rain  fell  in  one  month  than 
the  normal  annual  rainfall. 


TABLES 

SHOWING  MONTHLY,  SEASONAL  AND 
ANNUAL  RAINFALL 

1849-1911 


J I 


THE  RAINFALL. 

San  Francisco  Rainfall— Monthly,  1849-1880 


Year 

Jan. 

Feb. 

March 

AprU 

May 

June 

1850 

8.34 

1.77 

4.53 

0.46 

0 

0 

1851 

0.72 

0.54 

1.94 

1.23 

0.67 

0.02 

1852 

0.58 

0.14 

6.68 

0.26 

0.32 

0 

1853 

3.92 

1.42 

4.86 

5.37 

0.38 

0 

1854 

3.88 

8.04 

3.51 

3.12 

0.02 

0.08 

1855 

3.67 

4.77 

4.64 

5.00 

1.88 

0 

1856 

9.40 

0.50 

1.60 

2.94 

0.76 

0.03 

1857 

2.45 

8.59 

1.62 

0 

0.05 

0.12 

1858 

4.36 

1.83 

5.55 

1.55 

0.34 

0.05 

1859 

1.28 

6.32 

3.02 

0.27 

1.55 

0 

1860 

1.64 

1.60 

3.99 

3.14 

2.86 

0.09 

1861 

2.47 

3.72 

4.08 

0.51 

1.00 

0.08 

1862 

24.36 

7.53 

2.20 

0.73 

0.74 

0.05 

1863 

3.63 

3.19 

2.06 

1.61 

0.23 

0 

1864 

1.83 

0 

1.52 

1.57 

0.78 

0 

1865 

5.14 

1.34 

0.74 

0.94 

0.63 

0 

1866 

10.88 

2.12 

3.04 

0.12 

1.46 

0.04 

1867 

5.16 

7.20 

1.58 

2.36 

0 

0 

1868 

9.50 

6.13 

6.30 

2.31 

0.03 

0.23 

1869 

6.35 

3.90 

3.14 

2.19 

0.08 

0.02 

1870 

3.89 

4.78 

2.00 

1.53 

0.20 

0 

1871 

3.07 

3.76 

1.05 

1.89 

0.23 

0.01 

1872 

4.03 

6.90 

1.59 

0.81 

0.18 

0.04 

1873 

1.58 

3.94 

0.78 

0.43 

0 

0.02 

1874 

5.66 

2.21 

3.36 

0.90 

0.66 

0.14 

1875 

8.01 

0.32 

1.30 

0.10 

0.22 

1.02 

1876 

7.55 

4.92 

5.49 

1.29 

0.24 

0.04 

1877 

4.32 

1.18 

1.08 

0.26 

0.18 

0.01 

1878 

11.97 

12.52 

4.56 

1.06 

0.16 

0.01 

1879 

3.52 

4.90 

8.75 

1.89 

2.35 

0.05 

1880 

2.23 

1.87 

2.08 

10.06 

1.12 

0 

97 


98       THE  CLOUDS  AND  FOGS 
San  Francisco  Rainfall— Monthly,  1849-1879 


Year 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec 

1849 

0 

0 

0 

3.14 

8.66 

6.20 

1850 

0 

0 

0.33 

0 

0.92 

1.05 

1851 

0 

0.02 

1.03 

0.21 

2.12 

7.10 

1852 

0 

0 

0 

0.80 

5.31 

13.20 

1853 

0 

0.04 

0.46 

0.12 

2.28 

2.32 

1854 

0 

0.01 

0.15 

2.43 

0.34 

0.87 

1855 

0 

0 

0 

0 

0.67 

5.76 

1856 

0.02 

0 

0.07 

0.45 

2.79 

3.75 

1857 

0 

0.05 

0 

0.93 

3.01 

4.14 

1858 

0.05 

0.16 

0 

2.74 

0.69 

6.14 

1859 

0 

0.02 

0.03 

0.05 

7.28 

1.57 

1860 

0.21 

0 

0 

0.91 

0.58 

6.16 

1861 

0 

0 

0.02 

0 

4.10 

9.54 

1862 

0 

0 

0 

0.52 

0.15 

2.35 

1863 

0 

0 

0.03 

0 

2.55 

1.80 

1864 

0 

0.21 

0.01 

0.13 

6.68 

8.91 

1865 

0 

0 

0.24 

0.26 

4.19 

0.58 

1866 

0 

0 

0.11 

0 

3.35 

15.16 

1867 

0 

0 

0.04 

0.20 

3.41 

10.69 

1868 

0 

0 

0 

0.15 

1.18 

4.34 

1869 

0 

0 

0.12 

1.29 

1.19 

4.31 

1870 

0 

0 

0.03 

0 

0.43 

3.38 

1871 

0 

0.02 

0 

0.07 

2.81 

14.36 

1872 

0.01 

0 

0.04 

0.11 

2.79 

5.95 

1873 

0.01 

0.08 

0 

0.83 

1.16 

9.72 

1874 

0 

0 

0.02 

2.69 

6.55 

0.33 

1875 

0 

0 

0 

0.24 

7.27 

4.15 

1876 

0.01 

0.01 

0.38 

3.36 

0.25 

0« 

1877 

0.02 

0 

0 

0.65 

1.57 

2.66 

1878 

0.01 

T. 

0.55 

1.27 

0.57 

0.58 

1879 

0.01 

0.02 

T. 

0.78 

4.03 

4.46 

SAN  FRANaSCQ 


BSiiiliSiiiiSliiiiiiiS 


OF  SJN  FRANCISCO  101 

San  Francisco  Rainfall— Monthly,  1881-1915 


Year 

Jan. 

Feb. 

March 

April 

May 

June 

1881 

8.69 

4.65 

0.90 

2.00 

0.22 

0.69 

1882 

1.68 

2.96 

3.45 

1.22 

0.21 

0.04 

1883 

1.92 

1.04 

3.01 

1.51 

3.52 

0.01 

1884 

3.94 

6.65 

8.24 

6.33 

0.23 

2.57 

1885 

2.53 

0.30 

1.01 

3.17 

0.04 

0.19 

1886 

7.42 

0.24 

2.07 

5.28 

0.37 

0.01 

1887 

1.90 

9.24 

0.84 

2.30 

0.06 

0.07 

1888 

6.81 

0.94 

3.60 

0.11 

0.38 

0.27 

1889 

1.28 

0.72 

7.78 

0.96 

2.17 

0.03 

1890 

9.61 

5.16 

4.73 

1.18 

1.07 

0.10 

1891 

0.98 

7.26 

1.96 

2.44 

1.25 

0.11 

1892 

2.42 

2.90 

2.85 

1.39 

1.86 

T. 

1893 

3.05 

2.75 

4.08 

1.03 

0.15 

0.03 

1894 

5.99 

2.69 

0.60 

0.50 

1.31 

0.56 

1895 

6.99 

2.31 

1.89 

1.24 

0.60 

0 

1896 

8.14 

0.28 

2.85 

5.16 

0.72 

0 

1897 

2.26 

4.41 

4.56 

0.27 

0.61 

0.22 

1898 

1.12 

2.13 

0.24 

0.19 

1.44 

0.19 

1899 

3.67 

0.10 

7.61 

0.62 

0.86 

0.01 

1900 

4.11 

0.64 

1.91 

1.08 

0.32 

0.05 

1901 

5.79 

5.03 

0.80 

1.64 

0.69 

T. 

1902 

1.23 

7.27 

2.65 

0.98 

1.05 

T. 

1903 

3.73 

1.76 

6.23 

0.56 

T. 

T. 

1904 

1.05 

5.89 

6.01 

1.29 

0.30 

T. 

1905 

4.04 

2.70 

3.15 

1.33 

2.05 

0 

1906 

3.90 

4.30 

5.02 

0.92 

2.75 

0.56 

1907 

4.41 

3.02 

8.42 

0.11 

0.04 

1.28 

1908 

4.88 

5.39 

0.90 

0.22 

0.76 

0.01 

1909 

10.51 

7.53 

3.27 

T. 

T. 

T. 

1910 

3.24 

2.09 

3.78 

0.31 

0.03 

.02 

1911 

13.79 

3.02 

4.57 

0.89 

0.28 

.03 

1912 

.... 



.... 

.... 

.... 



1913 

.... 

1914 

.... 

1915 







102     THE  CLOUDS  AND  FOGS 
San  Francisco  Rainfall— Monthly,  1880-1915 


Year 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

1880 

0 

0 

0 

0.05 

0.33 

12.33 

1881 

0 

0 

0.25 

0.54 

1.94 

3.85 

1882 

0 

0 

0.26 

2.66 

4.18 

2.01 

1883 

0 

0 

0.42 

1.48 

1.60 

0.92 

1884 

T. 

0.04 

0.33 

2.55 

0.26 

7.68 

1885 

0.06 

T. 

0.11 

0.72 

11.78 

4.99 

1886 

0.23 

T. 

0.01 

1.48 

0.84 

2.07 

1887 

T. 

0.01 

0.29 

T. 

0.99 

3.34 

1888 

0.01 

0.01 

0.98 

0.13 

3.99 

5.80 

1889 

0.01 

T. 

T. 

7.28 

2.90 

13.81 

1890 

0.02 

0 

0.31 

0 

0 

3.25 

1891 

0.10 

0.02 

0.77 

0.04 

0.56 

5.62 

1892 

0 

0 

0.02 

1.65 

3.91 

5.08 

1893 

0.02 

0 

0.21 

0.16 

4.18 

2.25 

1894 

T. 

0 

1.05 

1.73 

0.88 

9.01 

1895 

0.01 

0 

0.77 

0.11 

1.78 

1.43 

1896 

0.04 

0.09 

0.52 

1.55 

4.56 

4.34 

1897 

T. 

T. 

0.10 

1.70 

1.05 

1.22 

1898 

0 

T. 

1.06 

0.86 

0.46 

1.62 

1899 

0 

T. 

0 

3.92 

3.79 

2.65 

1900 

T. 

T. 

0.46 

1.48 

3.91 

1.37 

1901 

T. 

T. 

0.78 

0.64 

3.48 

0.90 

1902 

T. 

T. 

T. 

1.70 

1.98 

2.32 

1903 

0 

T. 

T. 

0.17 

4.25 

1.63 

1904 

0.02 

0.06 

5.07 

2.37 

1.07 

1.59 

1905 

0 

T. 

T. 

T. 

0.92 

2.05 

1906 

0.08 

0.11 

0.18 

0.03 

1.59 

6.90 

1907 

T. 

0.02 

0.11 

1.36 

0.04 

3.66 

1908 

0.02 

0.01 

0.13 

0.61 

1.34 

2.15 

1909 

0 

T. 

0.80 

1.23 

2.43 

5.59 

1910 

T. 

0 

0.05 

0.65 

0.48 

1.73 

1911 

0 

0 

T 

.... 

.... 

1912 

.... 

.... 

.... 

.... 

1913 

.... 

.... 

.... 

.... 

1914 

.... 

.... 

.... 

.... 

1915 

.... 

.... 

.... 

.... 

.... 

.... 

OF  SJN  FRANCISCO 


105 


Seasonal  and  Annual  Rainfall— 1849-1911 


Seasonal 

Year 

Annual 

Seasonal 

Year 

Annual 

33.10 

1850 

17.40 

20.12 

1883 

15.43 

7.42 

1851 

15.60 

32.38 

1884 

38.82 

18.46 

1852 

27.29 

18.10 

1885 

24.90 

35.26 

1853 

21.17 

33.05 

1886 

20.02 

23.87 

1854 

22.45 

19.04 

1887 

19.04 

23.76 

1855 

26.39 

16.74 

1888 

23.03 

21.66 

1856 

22.31 

23.86 

1889 

36.94 

19.91 

1857 

20.96 

45.85 

1890 

25.43 

21.81 

1858 

23.46 

17.58 

1891 

21.11 

22.22 

1859 

21.39 

18.53 

1892 

22.08 

22.27 

1860 

21.18 

21.75 

1893 

17.91 

19.72 

1861 

25.52 

18.47 

1894 

24.32 

49.27 

1862 

38.63 

25.70 

1895 

17.13 

13.74 

1863 

15.10 

21.25 

1896 

28.25 

10.08 

1864 

21.64 

23.43 

1897 

16.40 

24.73 

1865 

14.06 

9.38 

1898 

9.31 

22.93 

1866 

36.28 

16.87 

1899 

23.23 

34.92 

1867 

30.64 

18.47 

1900 

15.33 

38.84 

1868 

30.17 

21.17 

1901 

19.75 

21.35 

1869 

22.59 

18.98 

1902 

19.18 

19.31 

1870 

16.24 

18.28 

1903 

18.33 

14.11 

1871 

27.53 

20.59 

1904 

24.72 

30.78 

1872 

22.42 

23.45 

1905 

16.24 

15.66 

1873 

18.56 

20.42 

1906 

26.34 

24.73 

1874 

22.52 

26.17 

1907 

22.47 

20.56 

1875 

22.63 

17.35 

1908 

16.42 

31.19 

1876 

23.54 

25.57 

1909 

31.36 

11.04 

1877 

11.93 

19.52 

1910 

12.38 

35.18 

1878 

33.26 

25.49 

1911 

24.44 

1879 

30.76 



1912 

26.66 

1880 

30.07 

1913 

29.86 

1881 

23.73 

1914 



16.14 

1882 

18.67 

1915 

Vfttft  /  Seasonal  is  from  July  1  to  June  30. 
•""**'  \  Annual  is  from  Jan.  1  to  Dec.  31 


106     THE  CLOUDS  AND  FOGS 
Average  Monthly  Rainfall— 1849-1911 


July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

Averages 

0.02 

0.02 

0.31 

1.02 

2.52 

4.59 

Jan. 

Feb. 

Mar. 

AprU 

May 

June 

Averages 

4.94 

3.60 

3.35 

1.65 

0.72 

0.02 

Average  Seasonal  Rainfall 

22.90  inches. 

Average  Annual  Rainfall 
22.66  inches. 


Kiosk 


THE  UNIVERSITY  LIBRARY 

UNIVERSITY  OF  CALIFORNIA,   SANTA  CRUZ 

SCIENCE  LIBRARY 

This  book  is  due  on  the  last  DATE  stamped  below. 


REC'DMAY  071986 


,.# 


NOV  19 '91 

NOV  19  1991 1't^  I 
OCT  IS  1992fiEC'D 


Series  24*; 


QC984.C2M3  Sci 


3  2106 


00242  9121 


p 


